Despite the availability of highly effective methods of contraception, a great number of pregnancies are unplanned, e.g. as a result of lack of access to contraceptives or contraceptive failure (such as condom slippage).
Emergency contraception (EC), by using a drug or device, is an important means of preventing unwanted pregnancy following sexual intercourse. Several approaches to emergency contraception have been described. Although the copper intrauterine device is the most effective EC method that can be used up to 5 days after the estimated time of ovulation, its widespread use is limited due to logistic and medical reasons. In the late 1970s Yuzpe introduced a regimen involving the combined use of oestrogen (0.1 mg ethinylestradiol) and progestogen (0.5 mg levonorgestrel) within 72 hours of the intercourse and repeated after 12 hours. The Yuzpe regimen was associated with a high incidence of nausea and vomiting due to the high oestrogen content. Since 1990s the potential of levonorgestrel (LNG), a synthetic progestogen, was recognised. Treatment with 0.75 mg LNG, repeated after 12 hours or as a single dose of 1.5 mg, within 72 hours of intercourse was shown to be associated with lower rate of side effects and higher efficacy than the Yuzpe regimen. However, if given when luteinizing hormone has already started to rise (LH surge), LNG lacks efficacy. The progesterone receptor modulator mifepristone (10 mg) offers another option for EC with very low side-effects and higher efficacy than the Yuzpe regimen. Also the interval between coitus and treatment could be extended to 120 hours with mifepristone. Yet another regimen is the treatment with the progesterone receptor modulator ulipristal acetate, which is more effective than LNG and which can be used up to 120 hours after intercourse.
There remains a need in the art for alternative methods of emergency contraception with reduced side-effects, which are effective in preventing unwanted pregnancy following intercourse, and which can be administered in a single effective dose, up to 120 hours after the intercourse.
The present invention now provides a new emergency contraceptive overcoming the above posed problems at least partially.